From the official release video:

New stuff includes (but is not limited to) tournament mode, correct video renderer (now with 100% more OpenGL), new audio backend, new enemy AI, new release types (e.g. windows ARM), and a kiloton of bugfixes and other minor features. It's been over ten years since the last release, so we got tired of trying to hunt down the full changelog ;)

Note that if you played the automated releases from github, then this probably does not have anything new to you. We just felt we had enough stuff for a new milestone. Also, note thet network play is still currently disabled, as we felt if requires more work before actual playtesting.